Linear actuator

ABSTRACT

A rotation-preventing slide is provided for a linear actuator which includes a housing which defines an internal bore and a piston-rod assembly which linearly moves within the internal bore in response to fluid pressure. The rotation-preventing slide is connected to and moves with the piston-rod assembly within a guide defined by the housing and has a geometry (e.g., polygonal, rectangular, square) which prevents rotation of the piston-rod assembly. The slide may include a bearing block and an attachment member which extends through an opening in the bearing block and which is removably attached to the piston-rod assembly whereby the slide&#39;s bearing surface (e.g., the bearing block) may be easily replaced. The guide may be a guide slot position parallel to, but axially offset from, the internal bore.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims to priority of provisional patentapplication Ser. No. 60/209,479 filed on Jun. 5, 2000 incorporated byreference.

FIELD OF THE INVENTION

This invention relates generally as indicated to a linear actuator and,more particularly, to a linear actuator having a slide for preventingrotation of the piston-rod assembly relative to the housing.

BACKGROUND OF THE INVENTION

In many manufacturing processes, individual sheet metal parts arefabricated with locating holes. Specifically, locating pins extendthrough these holes to hold the sheet metal parts in position relativeto each other and to the overall assembly during the welding process.Thus, accurate positioning of the locating pins is necessary to assureconsistent assembly.

In some situations, stationary locating pins may be fixed to the frameof the relevant manufacturing equipment. However, in many manufacturingsituations, the locating pins must be retracted from the completed sheetmetal assembly so that it can progress to the next station. In theselatter situations, the locating pin(s) are commonly mounted on a linearactuator.

A linear actuator typically comprises a housing which defines aninternal bore and a piston-rod assembly which moves within the internalbore in response to fluid pressure. One end of the rod is attached tothe piston. The other leading end of the rod (which extends beyond thehousing) includes pilot holes, flats and/or threaded passages forsecuring a locating pin thereto.

During the locating and/or welding process, it is important that thepiston-rod assembly not rotate relative to the housing. Thisnon-rotation is crucial to insuring that the working position of thelocating pin is reliable and repeatable. Rotational issues are magnifiedwhen it is necessary for a locating pin to be attached to an actuatorwith an offset in order to allow the pin to fit around some other partof the equipment during sheet metal working operations.

One technique traditionally used to prevent rotation of a piston-rodassembly in a linear actuator is provide the rod and correspondingbearing surface (of the internal bore) with a rotation-preventingcross-sectional geometry.

For example, the rod/bearing surface can be fabricated having a squarecross-sectional geometry. However, such polygonal arrangements aredifficult to fabricate in that consistently matching a square bearing toa square shaft in a high production environment is technicallychallenging. Additionally, even if fabrication issues are ignored, suchpolygonal arrangements tend to present wear problems. Specifically,whenever torque is applied to the shaft (as from an offset locating pin)the four corners of the shaft will continuously contact the bearingsurface thereby making these minimal areas of the rod extremelysusceptible to wear. Significantly, replacement of the worn partsusually requires disassembly of the housing components, disassembly ofthe piston-rod assembly, and replacement of the entire rod.

Another rotation-preventing cross-sectional geometry which is commonlyused is a round shaft with a circumference-interrupting flat and acircular bearing surface with a corresponding flat. This shaft design ismuch easier to manufacture than the square shaft because theflat-grinding process is controllable, even in a high productionenvironment. However, these shafts also tend to wear rapidly becausethere is only a single point of contact between the flat and the bearingwhen a torque is applied to the shaft. Again, significantly, replacementof the worn parts usually requires disassembly of the housingcomponents, disassembly of the piston-rod assembly, and replacement ofthe entire rod.

Instead of the rod, the piston of the piston-rod assembly, and thecorresponding piston chamber, may be made with a rotation-preventingshape. For example, the piston having an oval, rather than circularcross-sectional shape may be used thereby geometrically preventingrotation of the piston within its chamber. Again, significantly,replacement of the worn parts usually requires disassembly of thehousing components, disassembly of the piston-rod assembly, andreplacement of the entire piston.

Accordingly, the inventors appreciated that a need remains for arotation-preventing device which does not require non-circularpiston-rod components, which does not increase the axial length of theactuator, and/or which has bearing surfaces which may be easilyaccessed, inspected repaired, and/or replaced.

SUMMARY OF THE INVENTION

The present invention provides a rotation-preventing slide for a linearactuator which prevents rotation of the piston-rod assembly relative tothe housing. The rotation-preventing slide allows the use of standardcircular piston-rod components and does not include any axialextensions. Furthermore, the rotation-preventing slide, and particularlyits bearing surface, may be easily accessed, inspected, repaired and/orreplaced without disassembly of the piston-rod assembly, withoutdisassembly of the housing assembly, and/or without replacement of thepiston-rod components.

More particularly, the present invention provides a slide which isconnected to and moves with the piston-rod assembly within a guidedefined by the housing. The slide and guide each have a complimentaryrotation-preventing geometry thereby preventing rotation of thepiston-rod assembly. The rotation-preventing geometry may be polygonal,or more particularly rectangular, or even more particularly square.Because the rotation-preventing device of the present invention does notdepend upon the cross-sectional geometry of the piston-rod assembly, thepiston-rod assembly may comprises a rod and a piston having circularcross-sections.

The guide may be a guide slot positioned parallel to, but axially offsetfrom, the internal bore. If the housing comprises a rod end cap, acylindrical wall, and a rear end cap, the guide slot may be formed inthe rod end cap. In any event, because of the axial positioning of theslide, axial extensions of the piston-rod assembly are not necessary.

The slide may comprise a bearing block and an attachment member whichextends through an opening in the bearing block. The attachment membermay have a lower threaded portion which is screwed into a radialthreaded opening in the piston-rod assembly, or more particularly, therod.

In this manner, the slide's bearing surface (the bearing block) may bereplaced by simply unscrewing the attachment member, removing the usedbearing block from the guide, placing the new bearing block in theguide, and screwing the attachment member back into the piston-rodassembly. The bearing surface (i.e., the bearing block) of therotation-preventing slide is thus easily replaceable.

If the housing of the linear actuator includes an open-topped receptaclewhich is covered by a cover, the guide may constitutes a bottomextension of the receptacle. In this manner, an upper portion theattachment member would be positioned within the receptacle and easilyaccessible by removing the cover. If the linear actuator is to include asensor assembly to generate signals when the piston-rod assembly is atcertain positions, the rotation-preventing slide may incorporates thecertain components of the sensing assembly.

These and other features of the invention are fully described andparticularly pointed out in the claims. The following descriptiveannexed drawings set forth in detail a certain illustrative embodimentof the invention, this embodiment being indicative of but one of thevarious ways in which the principles of the invention may be employed.

DRAWINGS

FIG. 1 is a cross-sectional view of a linear actuator according to thepresent invention.

FIG. 2 is a top view of the linear actuator with its housing coverpartially removed and certain components of its anti-rotation deviceomitted.

DETAILED DESCRIPTION

Referring now to the drawings in detail, a linear actuator 10 accordingto the present invention is shown. The linear actuator 10 comprises ahousing 12 which defines an internal bore 14 and a piston-rod assembly16 which includes a rod 18 and a piston 20. Fluid supply lines (notshown) supply pressurized fluid to the actuator to linearly move thepiston-rod assembly 14 within the Internal bore 14 between the retractedposition shown in FIG. 1 and the extended position shown in phantom inFIG. 1.

The illustrated housing 12 comprises a rod end cap 30, a cylindricalwall 32, and a rear end cap 34. The rod end cap 30 includes a centrallylocated cylindrical passage 36 which is the leading part of the internalbore 14 and which is shaped, sized, and machined to allow smooth linearsliding of the rod 18 and thus functions as a bearing surface. Thecylindrical wall 32, together with the facing ends of the caps 20 and24, define a piston chamber 28 which is the rear part of the internalbore 14 and which is shaped, sized and machined to allow smooth linearsliding of the piston 20.

Seals may be employed between the housing components namely, forexample, O-ring seals 40 and 42 may be positioned in annular shouldersin the caps 30 and 34 to seal the cylinder wall 32 to the caps. Also, ascraper seal 44 may be positioned within an annular groove in the rodend cap 20 surrounding the outlet of the passage 36 and/or a U-cap seal46 may be positioned within an annular recess in the rod end cap 16.

The rod 18 of the piston-rod assembly 16 comprises a primary cylindricalportion 50 which slides within the bore 14 and a leading extensionportion 52. The leading end of the portion 50 is attached to theextension portion 52 and its rear end includes a stepped contour and acentral axial threaded opening 54. The extension portion 52 includespilot holes and various flats and threaded passages for securing alocating pin thereto.

The piston 20 of the piston-rod assembly 16 is generally annular andincludes a threaded central opening 56 surrounded by annular steppedridges. The piston 20 carries a pair of U-cap seals 58 incircumferential grooves. The seals 58 ride against the interior surfaceof the cylindrical wall 32 so that fluid pressure applied to one side ofthe piston 20 causes the piston-rod assembly 16 to move in one directionor the other without leakage between the piston 20 and the internalsurface of the cylinder 32.

The rod 18 and the piston 20 are connected together by a threadedattachment member 60 which extends through the openings 54 and 56. AnO-ring 62 may be used to seal the attachment between the rod 18 and thepiston 20. An axially central opening 64 in the rear end cap 34accommodates the head of the attachment member 50. A radially extendingchannel 64 with a threaded inlet communicates with the opening 66 forconnection to a fluid supply line.

The linear actuator 10 according to the present invention includes arotation-preventing slide 72 for preventing rotation of the piston-rodassembly 16, and particularly the rod 18, during operation. The slide 72is attached to the piston-rod assembly 16 for movement therewith. In theillustrated embodiment, the slide 72 comprises a cubical bearing block74 and an attachment member 76. The attachment member 76 extends througha circular core in the bearing block 74 and its lower threaded portionis attached to the rod 18. Specifically, the lower portion is screwedinto a radial threaded opening 78 in the rod 18 thereby attaching thebearing block 74 to the piston-rod assembly 16.

During retraction/extension of the piston-rod assembly 16, the slide 72travels within a guide 80. In the illustrated embodiment, the guide slot80 is formed in the rod end cap 30 and has a square cross-sectioncorresponding to the geometry of the bearing block 74. In any event, theguide 80 ensures that the slide 72 moves only linearly in the axialdirection of the piston-rod assembly 16. By preventing transversemovement of the slide 72, rotation of the piston-rod assembly 16 is alsoprevented.

In the illustrated embodiment, the rod end cap 30 defines an open-toppedreceptacle 82 which may be concealed by a cover 84. The guide 80constitutes a bottom extension of this receptacle 82 whereby an upperportion the attachment member 76 is positioned there within. Thus,access to the rotation-preventing slide 72 may be easily gained bysimply removing the cover 84 without disassembly of the housingcomponents 30, 32 and 34. Additionally, to inspect, repair and/orreplace the bearing block 74, one must simply unscrew the attachmentmember 76 and withdraw the bearing block 74 from the guide 80 wherebydisassembly of the rod 18 and piston 20 from each other and/or thehousing 12 is not necessary. Initial assembly, or re-assembly, of therotation-preventing slide 72 may be performed in the reverse manner. Inthis regard, it is noted that the rod 18 may include a plurality ofaxially aligned threaded openings 78 (such as four openings arranged 90°apart) for ease in initial assembly.

The receptacle 84 may also be used to house a sensing assembly 86 forthe actuator 10. Such a sensing assembly 86 may be desirable in certainapplications to generate a signal when the piston-rod assembly 16reaches either of its extreme positions and/or certain positionstherebetween. The illustrated embodiment of the invention allows therotation-preventing slide 72, and particularly the attachment member 76,to incorporate certain components of the sensing assembly 86 therebymaking their inspection, repair, and/or replacement also convenient. Forexample, satellite sensors 88 may be suspended within the receptacle 84to sense the position of the attachment member 76, and therefore thepiston-rod assembly 16. An opening 90 in the top surface of the rod endcap 30 may be used for attachment of a housing 92 of the for dataconnection.

Accordingly, one may now appreciate that the present invention providesa rotation-preventing slide which prevents rotation of the piston-rodassembly relative to the housing. The rotation-preventing slide may beused with standard circular piston-rod components and does not includeany axial extensions. Furthermore, the bearing surface of therotation-preventing slide may be easily accessed, repaired, and/orreplaced without disassembly of the piston-rod assembly and/or thehousing assembly.

Although the invention has been shown and described with respect to acertain embodiment, it is obvious that equivalent and obviousalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification. The presentinvention includes all such alterations and modifications and is limitedonly by the scope of the following claims.

1. A linear actuator comprising: a housing which defines an internalbore having a rear part forming a piston chamber, wherein thehousing-comprises a rod end cap, a cylindrical wall, and a rear end cap;a piston-rod assembly which linearly moves within the internal bore inresponse to fluid pressure and which includes a piston positioned withinthe piston chamber and a rod connected to the piston; a guide defined bythe housing, wherein the guide is a guide slot parallel with a portionof the internal bore which defines a bearing surface for the piston-rodassembly, and wherein the guide slot is formed in the rod end cap; abearing block, wherein the bearing block extends radially from the rodinto the guide, therein defining a bearing surface, wherein the bearingblock has a geometry to prevent rotation of the piston-rod assembly, andwherein the bearing block and the guide are separate from the pistonchamber; and an attachment member that extends through an opening in thebearing block, therein coupling the bearing block to the rod, whereinthe bearing block is operable to move with the piston-rod assembly.
 2. Alinear actuator as set forth in claim 1, wherein the rod has a circularcross-section and the piston has a circular cross-section.
 3. A linearactuator as set forth in claim 1, wherein the rotation-preventinggeometry is a geometry having a polygonal cross-section.
 4. A linearactuator as set forth in claim 3, wherein the rotation-preventinggeometry is a geometry having a rectangular cross-section.
 5. A linearactuator as set forth in claim 4, wherein the rotation-preventinggeometry is a geometry having a square cross-section.
 6. A linearactuator as set forth in claim 1, wherein the attachment member has alower threaded portion which is screwed into a radial threaded openingin the piston-rod assembly.
 7. A linear actuator as set forth in claim6, wherein the rod includes the radial threaded opening, and wherein thelower portion of the attachment member is screwed into the radialthreaded opening in the rod.
 8. A linear actuator as set forth in claim1, wherein the bearing block is removably attached to the piston-rodassembly.
 9. A linear actuator as set forth in claim 8, wherein thebearing block linearly moves within the guide during movement of thepiston-rod assembly.
 10. A linear actuator as set forth in claim 1,further comprising a sensor assembly to generate signals when thepiston-rod assembly is at certain positions and wherein the attachmentmember incorporates certain components of the sensor assembly.
 11. Alinear actuator as set forth in claim 1, wherein the guide slot axiallyoffset from the internal bore.
 12. A linear actuator as set forth inclaim 1, wherein the guide and the bearing block are positioned a radialdistance from the rod which is less than the diameter of the pistonchamber.
 13. A linear actuator as set forth in claim 1, wherein thehousing defines an open-topped receptacle which is covered by a cover,wherein the guide constitutes a bottom extension of the receptacle, andwherein an upper portion the attachment member is positioned within thereceptacle.
 14. A method of inspecting and/or removing the bearing blockof the linear actuator of claim 13, comprising the steps of: uncoveringthe receptacle; unscrewing the attachment member; withdrawing theattachment member from the bearing block; and removing the bearing blockfrom the guide.
 15. A method of installing and/or re-installing thebearing block of the linear actuator of claim 13, comprising the stepsof: inserting the bearing block into the guide; inserting the attachmentmember through the opening in the bearing block; and screwing theattachment member to the piston-rod assembly.
 16. A linear actuator,comprising: a housing, wherein the housing defines an internal bore, theinternal bore having a rear part forming a piston chamber; a pistonpositioned within the piston chamber, the piston being connected to arod, wherein the rod comprises a plurality of radial threaded openingspositioned about a circumference thereof, and wherein the piston isoperable to linearly translate within the internal bore in response tofluid pressure, therein linearly translating the rod; a guide, whereinthe guide is defined by the housing, and wherein the guide is separatefrom the piston chamber; and a bearing block removably coupled to therod and operable to linearly translate therewith, wherein the bearingblock radially extends from the rod into the guide, and wherein thebearing block has a polygonal geometry that slidingly mates to theguide, therein defining a bearing surface, therein preventing a rotationof the rod; and an attachment member having a threaded portion, whereinthe attachment member extends through an opening in the bearing blockinto the rod, therein removably coupling the bearing block to the rod,and, wherein the threaded portion of the attachment member is operableto be screwed into any of the plurality of radial threaded openings. 17.The linear actuator of claim 16, wherein the rod comprises four radialthreaded openings spaced 90° about the circumference of the rod.
 18. Thelinear actuator of claim 16, wherein the bearing block has a rectangularcross-section when viewed radially from the rod.
 19. The linear actuatorof claim 18, wherein the bearing block has a square cross-section whenviewed radially from the rod.
 20. The linear actuator of claim 16,further comprising a sensor assembly, wherein the attachment memberfurther comprises at least a portion of the sensor assembly, wherein thesensor assembly is operable to generate signals when the rod is atcertain positions.
 21. The linear actuator of claim 16, wherein thehousing further generally defines an open-topped receptacle, wherein abottom extension of the receptacle is generally defined by the guide.22. The linear actuator of claim 21, further comprising a cover, whereinthe cover is removably attached to the open-topped receptacle, thereinselectably concealing the guide.
 23. The linear actuator of claim 16,wherein the guide is parallel to, but axially offset from, the internalbore.
 24. A linear actuator, comprising: a housing, wherein the housingdefines an internal bore, the internal bore having a rear part forming apiston chamber; a piston positioned within the piston chamber, thepiston being connected to a rod, wherein the rod comprises a primarycylindrical portion and an extension portion which are coaxial with oneanother, wherein the primary cylindrical portion generally resideswithin the internal bore, and wherein the extension portion generallyresides external to the housing, wherein the extension portion furthercomprises one or more of pilot holes, flats, and threaded passages forsecuring a locating pin thereto, and wherein the piston is operable tolinearly translate within the internal bore in response to fluidpressure, therein linearly translating the rod; a guide, wherein theguide is defined by the housing, and wherein the guide is separate fromthe piston chamber; and a bearing block removably coupled to the rod andoperable to linearly translate therewith, wherein the bearing blockradially extends from the rod into the guide, and wherein the bearingblock has a polygonal geometry that slidingly mates to the guide,therein defining a bearing surface, therein preventing a rotation of therod.
 25. A linear actuator comprising: a housing which defines aninternal bore having a rear part forming a piston chamber; a piston-rodassembly which linearly moves within the internal bore in response tofluid pressure and which includes a piston positioned within the pistonchamber and a rod connected to the piston, wherein the rod comprises aprimary cylindrical portion and an extension portion which are coaxialwith one another, wherein the primary cylindrical portion generallyresides within the internal bore, and wherein the extension portiongenerally resides external to the housing, wherein the extension portionfurther comprises one or more of pilot holes, flats, and threadedpassages for securing a locating pin thereto; a guide defined by thehousing; a bearing block, wherein the bearing block extends radiallyfrom the rod into the guide, therein defining a bearing surface, whereinthe bearing block has a geometry to prevent rotation of the piston-rodassembly, and wherein the bearing block and the guide are separate fromthe piston chamber; and an attachment member that extends through anopening in the bearing block, therein coupling the bearing block to therod, wherein the bearing block is operable to move within the piston-rodassembly.